Nitrous oxide-induced NO-dependent neuronal release of β-endorphin from the rat arcuate nucleus and periaqueductal...

Nitrous oxide (N(2)O)-induced antinociception is thought to result from nitric oxide (NO)-dependent neuronal release of endogenous opioid peptides in the central nervous system. The present study employed microdialysis to determine whether exposure to N(2)O stimulates proopiomelanocortin (POMC) neurons to release β-endorphin in the arcuate nucleus (ARC) of the hypothalamus and the periaqueductal gray (PAG) of the midbrain. Male Sprague-Dawley rats were stereotaxically implanted with microdialysis probes in the ARC or PAG. Exposure to 70% N(2)O significantly increased dialysate levels of oxidation products of NO as well as β-endorphin, compared to levels in fractions collected under room air. These increases in the ARC and PAG were abolished by systemic pretreatment with L-N(G)-nitro arginine methyl ester (L-NAME). These findings suggest an association between increased NO activity and the stimulated release of β-endorphin during exposure of rats to N(2)O.